The invention concerns a device for measurement of surfaces and a method for operation of a device, in which the device has a light source to generate a multicolor light beam, the light beam being focusable by imaging optics, using chromatic aberration of the optics, on several points at different distance from the imaging optics, in which the focused light beam can be controlled on the surface and a sensor device is provided to detect the reflected light beam.
In many areas of engineering it is important to have precise knowledge concerning the condition of surfaces. Burrs or waviness of the surface that can form during production of objects are only tolerable in many applications in very narrow limits. Especially in high-precision mechanisms with moving parts, insufficient surface quality can lead to improper function or rapid destruction. In addition to gaining information on the quality of the surface, in many areas, precise measurement of structures in a surface is required. For example, in many applications, it is of interest to know the depths and position of millings or holes in a work piece.
Different methods for measuring surfaces are known from practice. In one possible method, two or more cameras are used, with which information concerning the three-dimensional condition of the surface is calculated by triangulation. However, only very restricted measurement accuracies can be achieved with such measurement systems.
In another method known from practice, a monochromatic light beam is guided to a surface being investigated, in which the light beam is always focused on the surface. If a distance between the optics and the illuminated image point changes as a result of surface unevenness and the light beam is therefore no longer focused on the surface, an automatic focusing circuit regulates the optics, so that the light beam is refocused on the surface. From the degree of adjustment of the optics, the distance change can be determined. In this way, the surface can be measured relatively precisely, but the measurement speed is severely restricted because of necessary adjustment of the optics. Measurement of the surface in a running production process is therefore not feasible.
To avoid this adjustment, a method is known, with which surfaces can be measured by the use of multicolor light (mostly white light) and using chromatic aberration. The fact that the focus of the imaging optics depends on the wavelength of the light is utilized in this case. If a light beam focused on several foci impinges on a surface, the light beam is reflected from it. The spectral fractions, whose focus was not in the region of the surface during reflection, are essentially suppressed or blocked out via an aperture device or glass fiber. Because of this, the distance of the optics from the illuminated point of the surface can be determined by spectral analysis of the light beam processed in this way. Relatively large measurement speeds can be achieved, but the spacing between the optics and the measurement object is subject to very sharp restrictions. During use of lenses with very short focal lengths, during a spacing change to the surface of the object being measured, a relatively strong shift in the detected spectrum is obtained and therefore relatively high measurement accuracy or resolution, but the attainable measurement distance is significantly reduced—i.e., the distance between the sensor and the object being measured. If lenses with a larger focal length are used, larger measurement spacings and measurement areas can be achieved, but the measurement accuracy or resolution of the arrangement significantly diminishes.
The underlying task of the present invention is therefore to configure and modify a device of the type just mentioned, so that a high-resolution measurement of surfaces, as quickly and simply as possible, can be achieved with the largest possible distance between the optics and the measurement object and the simplest design of the measurement device at the same time. In addition, a corresponding method is to be provided.